Petroleum is an extremely complex mixture and consists predominantly of hydrocarbons, as well as compounds containing nitrogen, oxygen, and sulfur. Most petroleums also contain minor amounts of nickel and vanadium. The chemical and physical properties of petroleum vary considerably because of variations in petroleum composition.
Gasoline is a complex mixture of hydrocarbons. Commercial gasolines are blends of straight-run, cracked, reformed, and natural gasolines. Straight-run gasoline is recovered from crude petroleum by distillation and contains a large proportion of normal hydrocarbons of the paraffin series. Cracked gasoline is manufactured by heating crude-petroleum distillation fractions or residues under pressure, or by heating with or without pressure in the presence of a catalyst. Heavier hydrocarbons are broken into smaller molecules, some of which distill in the gasoline range. Reformed gasoline is made by passing gasoline fractions over catalysts in such a manner that low-octane-number hydrocarbons are molecularly rearranged to high-octane-number components. Many of the catalysts use platinum and other metals deposited on a silica and/or alumina support. Natural gasoline is obtained from natural gas by liquefying those constituents which boil in the gasoline range either by compression and cooling or by absorption in oil. During the production of gasoline, the processing of crude petroleum products can become fouled with contaminants, including polar molecule contaminants.
Many polar organic compounds such as S-containing molecules, naphthenic acid, asphaltene, porphyrin, and N-containing molecules add negative value to oil and its products. The negative value is associated with the costly refining and processing of these polar molecules due to their role played in corrosion, fouling, catalyst poisoning, and emissions. Therefore, safe and cost effective removal of polar molecules from hydrocarbon and chemical streams significantly increases energy savings and process profitability.
One method to remove polar molecules from a fluid is to flow the liquid through a fixed bed of particles which adsorb the polar molecules. However, a fixed bed process generally precludes the use of very small adsorbent particles that are less than 0.5 or 1.0 mm in size because of the excessive pressure drop that will result in a commercial process when such particles are used. This high pressure drop becomes even a bigger concern if the fixed bed fouls and plugs up.
Additionally, a fixed bed process requires periodic regeneration of the fixed bed following use, which is difficult and costly to achieve. For example, a high temperature is required to regenerate the fixed bed such that the bed is again able to adsorb particle contaminants. Due to the poor thermal conductivity and large size (e.g., several feet in diameter) of commercial fixed beds, regeneration usually requires heating the bed for several hours to achieve a temperature high enough to regenerate the bed. The time periods required for regeneration of fixed beds thus results in an industrial operation that is not practical or economical.